fractal/palette.c

/*
 * fractal
 * Written in 2020 by Lucas
 * CC0 1.0 Universal/Public domain - No rights reserved
 *
 * To the extent possible under law, the author(s) have dedicated all
 * copyright and related and neighboring rights to this software to the
 * public domain worldwide. This software is distributed without any
 * warranty. You should have received a copy of the CC0 Public Domain
 * Dedication along with this software. If not, see
 * <http://creativecommons.org/publicdomain/zero/1.0/>.
 */
/* gepopt visibility for GLIBC */
#if !defined(__OpenBSD__)
#define _DEFAULT_SOURCE
#endif

#include <limits.h>
#include <stdlib.h>
#include <unistd.h>

#include "palette.h"
#include "pnmout.h"
#include "util.h"

#define CLAMP(x, a, b) ((x) < (a) ? (a) : (x) > (b) ? (b) : (x))

static double
bezier3(double t, double p0, double p1, double p2, double p3)
{
	double u = 1.0 - t;
	return u * u * u * p0
	    + 3.0 * u * u * t * p1
	    + 3.0 * u * t * t * p2
	    + t * t * t * p3;
}

static double
bezier4(double t, double p0, double p1, double p2, double p3)
{
	return (1.0 - t) * bezier3(t, p0, p1, p2, p3)
	    + t * bezier3(t, p1, p2, p3, p0);
}

struct color *
palette_gen(size_t n)
{
	struct color *palette;
	double p[12] = {
		drand48(), drand48(), drand48(),
		drand48(), drand48(), drand48(),
		drand48(), drand48(), drand48(),
		drand48(), drand48(), drand48(),
	};
	double r, g, b, t;
	size_t i;

	if ((palette = malloc(n * sizeof(*palette))) == NULL)
		errx(1, "out of memory");

	for (i = 0; i < n; i++) {
		t = i / (double)n;
		r = bezier4(t, p[0], p[3], p[6], p[9]);
		g = bezier4(t, p[1], p[4], p[7], p[10]);
		b = bezier4(t, p[2], p[5], p[8], p[11]);
		palette[i].r = 65535.0 * CLAMP(r, 0.0, 1.0);
		palette[i].g = 65535.0 * CLAMP(g, 0.0, 1.0);
		palette[i].b = 65535.0 * CLAMP(b, 0.0, 1.0);
	}

	return palette;
}

static void
usage(void)
{
	fprintf(stderr, "Usage: %s palette [-h height] [-w width]\n",
	    xgetprogname());
	exit(1);
}

int
palette_main(int argc, char *argv[])
{
	struct color *palette;
	int ch, i, j, width, height;

	height = 50;
	width = 500;
	while ((ch = getopt(argc, argv, "h:w:")) != -1)
		switch (ch) {
		case 'h':
			height = parse_integer(optarg, 1, 65535);
			break;
		case 'w':
			width = parse_integer(optarg, 1, 65535);
			break;
		default:
			usage();
		}
	argc -= optind;
	argv += optind;

	if (argc > 1)
		usage();

	palette = palette_gen(width);
	pnmout_header(stdout, width, height);
	for (i = 0; i < height; i++)
		for (j = 0; j < width; j++)
			pnmout_pixel(stdout, palette[j]);
	free(palette);

	return !(fflush(stdout) == 0);
}